HT46R49 Holtek Semiconductor, HT46R49 Datasheet - Page 42

• Manufacturer Part Number: HT46R49
• Description: Cost-Effective A/D Type 8-Bit MCU
• Manufacturer: Holtek Semiconductor

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Oscillator
Various oscillator options offer the user a wide range of
functions according to their various application require-
ments. Two types of system clocks can be selected
while various clock source options for the Watchdog
Timer are provided for maximum flexibility. All oscillator
options are selected through the configuration options.
The two methods of generating the system clock are:
One of these two methods must be selected using the
configuration options.
More information regarding the oscillator is located in
Application Note HA0075E on the Holtek website.
External Crystal/Resonator Oscillator
The simple connection of a crystal across OSC1 and
OSC2 will create the necessary phase shift and feed-
back for oscillation, and will normally not require exter-
nal capacitors. However, for some crystals and most
resonator types, to ensure oscillation and accurate fre-
quency generation, it may be necessary to add two
small value external capacitors, C1 and C2. The exact
values of C1 and C2 should be selected in consultation
with the crystal or resonator manufacturer s specifica-
tion. The external parallel feedback resistor, Rp, is nor-
mally not required but in some cases may be needed to
assist with oscillation start up.
Rev. 1.30
External crystal/resonator oscillator
External
Internal Ca, Cb, Rf Typical Values @ 5V, 25°C
11~13pF
Oscillator Internal Component Values
Ca
RC oscillator
Crystal/Resonator Oscillator
13~15pF
Cb
470k
Rf
HT46R46/C46/R47/C47/R48A/C48A/R49
42
External RC Oscillator
Using the external system RC oscillator requires that a
resistor, with a value between 24k
nected between OSC1 and ground, and a capacitor is
connected to VDD. The generated system clock divided
by 4 will be provided on OSC2 as an output which can
be used for external synchronization purposes. Note
that as the OSC2 output is an NMOS open-drain type, a
pull high resistor should be connected if it to be used to
monitor the internal frequency. Although this is a cost ef-
fective oscillator configuration, the oscillation frequency
can vary with VDD, temperature and process variations
and is therefore not suitable for applications where tim-
ing is critical or where accurate oscillator frequencies
are
refer to the Holtek website for typical RC Oscillator vs.
Temperature and VDD characteristics graphics.
that it is the only microcontroller internal circuitry to-
gether with the external resistor, that determine the fre-
quency of the oscillator. The external capacitor shown
on the diagram does not influence the frequency of os-
cillation.
Crystal Frequency
8MHz
4MHz
1MHz
Note: 1. C1 and C2 values are for guidance only.
Resonator Frequency
3.58MHz
1MHz
455kHz
Note: C1 and C2 values are for guidance only.
required.For the value of the external resistor R
Resonator Recommended Capacitor Values
Crystal Recommended Capacitor Values
Crystal Oscillator C1 and C2 Values
2. CL is the crystal manufacturer specified
load capacitor value.
Resonator C1 and C2 Values
RC Oscillator
TBD
TBD
TBD
C1
TBD
TBD
TBD
C1
TBD
TBD
TBD
and 1M , is con-
C2
June 5, 2008
TBD
TBD
TBD
C2
TBD
TBD
TBD
CL
Note
OSC